In such an electric power supply system for supplying power generated by an AC generator to a load having an electric storage device, the following configuration has been disclosed. That is, the electric power supply system includes: an AC generator having a drooping characteristic in which output voltage decreases along with increase in load while output power increases to become maximum at the maximum power operation point, and then the output voltage further decreases while the output power decreases; and a DC/DC converter as a control section for adjusting the output voltage of the AC generator. Then, the AC generator is controlled so as to operate on the low-current side relative to output current corresponding to the maximum power operation point of the AC generator, that is, on the high-voltage side relative to the output voltage corresponding to the maximum power operation point (for example, see Patent Document 1).